Method for managing key in DRM system

PURPOSE: A method for managing a key in a digital CONSTITUTION: A commerce system(Retailer,12) packages contents using a packager(13). A consumer system(14) purchases contents from the commerce system(12). The commerce system(12) downloads the selected contents and requests a license from a clearinghouse(11). The clearinghouse(11) downloads a corresponding license to the consumer system(14). A Core-ID of the corresponding contents exists in a license file, and a Retailer-ID is included in a content header supplied from the commerce system(12). A player collects the Core-ID of the license file and the Retailer-ID of a contents file, creates a symmetric key in the consumer system(14), and decodes/operates coded contents using the created symmetric key.